HERSCHEL SPACE OBSERATORY

July 1, 2013

“Two men look out of the same prison bars; one sees mud and the other stars.”

For centuries and centuries men have looked up—seen the stars, wondered about their creation and pondered traveling to distant planets and star systems. The action of the two prisoners above indicates interest by one and no interest from the other in “all things celestial”. The real truth is, just about everyone in every country is fascinated with the cosmos. Events leading up to the creation lie in the stars. No doubt about it.

One significant effort to unwrap the truth was undertaken by the ESA (European Space Agency) in launching the Herschel Space Observatory on May 14, 2009. The Herschel Space Observatory is named after Sir William Herschel and is the fourth Cornerstone mission in the European Space Agency’s Horizon 2000 program. Ten countries, including the United States, participated in its design and implementation. Sir William and his sister, Caroline collaborated in discovering theinfrared spectrum in 1800 and the planet Uranus. That spectrum extends beyond visible light into the region that we today call “infrared.” The far-infrared and sub-millimeter wavelengths at which Herschel observations are made are considerably longer than the familiar rainbow of colors that the human eye can perceive. Yet, this is a critically important portion of the spectrum to scientists because it is the frequency range at which a large part of the universe radiates. Much of the universe consists of gas and dust far too cold to radiate in visible light or at shorter wavelengths such as x-rays. However, even at temperatures well below the most frigid spot on earth, they do radiate at far-infrared and sub-millimeter wavelengths.

Stars and other cosmic objects not hot enough to shine at optical wavelengths are often hidden behind vast dust clouds that absorb visible light and reradiate that light in the far-infrared and sub-millimeter.

There is a great deal to see at these wavelengths, and much of it has been virtually unexplored. Earthbound telescopes are largely unable to observe this portion of the spectrum because most of this light is absorbed by moisture in the atmosphere before it can reach the ground. Previous space-based infrared telescopes have had neither the sensitivity of Herschel’s large mirror, nor the ability of Herschel’s three detectors to do such a comprehensive job of sensing this important part of the spectrum.

Two-thirds of Herschel’s observation time has been made available to the world scientific community, with the remainder reserved for the spacecraft’s science and instrument teams. The flood of data from Herschel makes it impractical for multiple websites to provide up-to-date or reasonably complete information about all of the observations that have been carried out and published in scientific journals.

Well—we knew it was coming but, it is still sad to see the end of a mission. Controllers for the Herschel space telescope sent final commands today to put the observatory into a heliocentric parking orbit. Commands were sent at 12:25 GMT on June 17, 2013, marking the official end of operations for Herschel. But expect more news from this spacecraft’s observations, as there is still a treasure trove of data that that will keep astronomers busy for many years to come. Additionally, maneuvers done by the spacecraft allowed engineers to test control techniques that can’t normally be tested in-flight. Herschel’s science mission had already ended in April when the liquid helium that cooled the observatory’s instruments ran out.

Herschel will now be parked indefinitely in a heliocentric orbit, as a way of “disposing” of the spacecraft. It should be stable for hundreds of years, but perhaps scientists will figure out another use for it in the future. One original idea for disposing of the spacecraft was to have it impact the moon, a la the LCROSS mission that slammed into the Moon in 2009, and it would kick up volatiles at one of the lunar poles for observation by another spacecraft, such as the Lunar Reconnaissance Orbiter. But that idea has been nixed in favor of the parking orbit.

Some of the maneuvers that were tested before the spacecraft was put into its final orbit were some in-orbit validations and analysis of hardware and software.

On May 13-14, engineers commanded Herschel to fire its thrusters for a record 7-hours and 45-minutes. This ensured the satellite was boosted away from its operational orbit around the L2 Sun–Earth Lagrange Point and into a heliocentric orbit, further out and slower than earth’s orbit. This depleted most of the fuel, and the final thruster command today used up all of the remaining fuel. Today’s final command was the last step in a complex series of flight control activities and thruster maneuvers designed to take Herschel into a safe disposal orbit around the sun; additionally all its systems were turned off.

“Herschel has not only been an immensely successful scientific mission, it has also served as a valuable flight operations test platform in its final weeks of flight. This will help us increase the robustness and flexibility of future missions operations,” said Paolo Ferri, ESA’s Head of Mission Operations. “Europe really received excellent value from this magnificent satellite.”

Let’s now take a look at the results from the years of observation. Hope you enjoy just a very few of the pictures beamed back to Earth. I welcome your comments.